A major portion of recent development efforts in laser diodes have focused on increasing the power output available for applications such as solid state laser pumping or materials processing. Although some success has been achieved, the power output of diode lasers remains limited, primarily by the heat generated and the degradation of the output window. In general these problems are approached by attempting to improve laser efficiency and by enlarging the output window, but conventional semiconductor laser designs appear to have largely reached the limits of these improvements. It is the purpose of this invention to provide a unique laser diode structure having both enhanced efficiency and higher output power.
A typical diode laser consists of an assembly of layers of semiconductor materials which form a junction at their interface. On one side of the junction there is a relative absence of electrons (p) and at the other side of junction there is a relative excess of electrons (n). An electrical potential is applied across the junction to initiate (pump) electrons across the junction. With certain materials, the electron migration produces a population inversion, during which energy is released in the form of photons. The photons may be processed within a variety of elements of the laser diode and emitted as a laser beam. The region which comprises the junction is called the active layer and is defined by the so called p and n materials. In order to sustain and enhance the population inversion, the active region is limited by reflective elements which contain the photons within a portion of the active region called the laser cavity. These reflective elements vary in the degree of reflectivity to provide feedback of a percentage of the photons to the laser cavity and to transmit a portion of the incident photons from an edge of the diode or from the surface of the diode in a coherent laser beam.
The use of diodes having an edge emitting characteristic is limited because of the physical area available for the output window. On the other hand, the surface emitting diode is not so restricted and it is a purpose of this invention to make use of a surface emitting diode configuration in an enhanced power design.
In order to provide sufficient feedback and to deflect the laser light through the surface of the semiconductor, the active layer is confined between gratings having predetermined indexes of refraction. The gratings provide distributed feedback within the active layer and at least one of the gratings is defined to allow the transmission (coupling) of light in a deflected angle to a window which may be etched in the semiconductor surface. A laser cavity is formed generally within the active layer by the path of the current flow through the region. Therefore, by adjusting the conductivity of certain regions of the semiconductor, the current flow path, i.e., the laser cavity, may be defined advantageously.